Are the Lannisters okay with the Bo,tons accepting the Karstarks back into the fold or are they not aware of it?

neothoron:

racefortheironthrone:

They would care why?

I would guess, because Rickard Karstark had killed Willem Lannister and Tion Frey, two kin of House Lannister, and they may be angry because of that.

I would reply that:
* House Lannister may not even know that Cregan Karstark is currently a Bolton spy (Roose would have no reason to tell them)
* House Karstark had already paid for that act, with Robb’s execution of Rickard Karstark
* After nearly 40 years of Tywin being effective head of House Lannister, House Lannister has no moral standing to accuse another noble House of war crimes
* Roose and the Lannisters are expecting to be in competition, if not in conflict, when Spring comes – hard to see Roose caring about potential Lannister censure if he succeeds in pacifying the North

Ah, I gotcha. I mean, Kevan might care, but Tywin knows that Roose needs the Karstark infantry to make the Red Wedding happen and that takes priority over subsidiary Lannisters…for the moment.

Keep in mind, Tywin fully intended to betray Roose once he had no future use for him, because Lannisters pay their debts at a time of their convenience.